WO2024090483A1

WO2024090483A1 - Structure, method for producing structure, oil-resistant paper, gas barrier paper, flavor barrier paper and packaging material

Info

Publication number: WO2024090483A1
Application number: PCT/JP2023/038537
Authority: WO
Inventors: 歩山本; 悠太田岡
Original assignee: 株式会社クラレ
Priority date: 2022-10-27
Filing date: 2023-10-25
Publication date: 2024-05-02

Abstract

The present invention provides: a structure which is suppressed in cracking of a layer that has heat sealing properties, while having excellent water vapor barrier properties, heat sealing properties and oxygen barrier properties; a method for producing this structure; and oil-resistant paper, gas barrier paper, flavor barrier paper and a packaging material, each of which uses this structure. This structure is obtained by sequentially superposing a layer A, a layer B and a layer C in this order on at least one surface of a paper base material; the layer A contains at least one polymer that is selected from the group consisting of an olefin polymer, a styrene polymer and a polyester polymer; the layer B contains a vinyl alcohol polymer; and the layer C contains a polymer that has a glass transition temperature of -100°C to 5°C.

Description

Structure, method for manufacturing structure, greaseproof paper, gas barrier paper, flavor barrier paper, and packaging material

The present invention relates to a structure, a method for manufacturing a structure, grease-resistant paper, gas barrier paper, flavor barrier paper, and packaging materials.

In packaging food, medical products, electronic components, etc., packaging materials in which water vapor barrier properties and gas barrier properties (particularly oxygen barrier properties) have been imparted to a paper base material have been used for some time. Patent documents 1 and 2 describe packaging materials in which a water vapor barrier layer, a gas barrier layer, and a heat seal layer are provided in that order on a paper base material. Patent documents 1 and 2 also describe packaging materials such as the above in which a vinyl alcohol-based polymer is used for the gas barrier layer.

JP 2020-163675 A JP 2021-20398 A

In packaging materials such as those described in Patent Documents 1 and 2, each layer is generally provided on a paper base material by coating. However, when a heat seal layer is provided on the surface of a gas barrier layer containing a vinyl alcohol polymer, cracks may occur in the formed coating, making it difficult to obtain uniform heat sealability. The inventors have also found that cracks in the heat seal layer can cause a decrease in water vapor barrier properties.

The present invention aims to provide a structure that has little cracking in the heat-sealable layer and has excellent water vapor barrier properties, heat-sealability and oxygen barrier properties, a method for manufacturing such a structure, and grease-resistant paper, gas barrier paper, flavor barrier paper and packaging materials that use such a structure.

The above issues are:
[1] A structure in which an A layer, a B layer and a C layer are laminated in this order on at least one surface of a paper base material, the A layer containing at least one polymer selected from the group consisting of an olefin-based polymer, a styrene-based polymer and a polyester-based polymer, the B layer containing a vinyl alcohol-based polymer, and the C layer containing a polymer having a glass transition temperature of -100°C or more and 5°C or less;
[2] The structure according to [1], wherein the C layer has a melting point of 120° C. or less.
[3] The structure according to [1] or [2], wherein the layer A contains the olefin-based polymer, and the olefin-based polymer contains an olefin-unsaturated carboxylic acid-based polymer;
[4] The structure of [1], [2] or [3], wherein the layer A further contains talc;
[5] The structure according to [4], wherein the content of the talc in the layer A is 1% by mass or more and 80% by mass or less;
[6] The structure according to any one of [1] to [5], wherein the vinyl alcohol polymer is an ethylene-modified vinyl alcohol polymer;
[7] The structure according to any one of [1] to [6], wherein the polymer having a glass transition temperature of −100° C. or more and 5° C. or less is a styrene-acrylic copolymer;
[8] The structure according to any one of [1] to [7], wherein the C layer further contains a wax;
[9] The structure according to [8], wherein the content of the wax in the layer C is 0.1% by mass or more and 30% by mass or less;
[10] The structure of [8] or [9], wherein the wax comprises paraffin wax;
[11] The structure according to [10], wherein the content of the paraffin wax in the layer C is 1% by mass or more and 30% by mass or less;
[12] The structure according to any one of [1] to [11], wherein the vinyl alcohol polymer comprises two or more kinds of vinyl alcohol polymers having different degrees of polymerization;
[13] The structure according to any one of [1] to [12], wherein the layer A contains at least two polymers selected from the group consisting of the olefin-based polymer, the styrene-based polymer, and the polyester-based polymer;
[14] The structure according to any one of [1] to [13], wherein the C layer contains two or more types of polymers;
[15] A method for producing a structure according to any one of [1] to [14], comprising providing at least one of the A layer, the B layer, and the C layer using a curtain coater;
[16] Greaseproof paper comprising any one of the structures according to [1] to [14];
[17] A gas barrier paper comprising any one of the structures according to [1] to [14];
[18] A flavor barrier paper comprising any one of the structures according to [1] to [14];
[19] A packaging material comprising at least one selected from the group consisting of the greaseproof paper of [16], the gas barrier paper of [17], and the flavor barrier paper of [18];
The problem is solved by providing either

The present invention provides a structure that has little cracking in the heat-sealable layer and has excellent water vapor barrier properties, heat-sealability, and oxygen barrier properties, a method for manufacturing such a structure, and grease-resistant paper, gas barrier paper, flavor barrier paper, and packaging materials that use such a structure.

FIG. 1 is a schematic cross-sectional view showing a structure according to one embodiment of the present invention.

<Structure>
A structure according to one embodiment of the present invention is a structure in which an A layer, a B layer, and a C layer are laminated in this order on at least one surface of a paper base material, the A layer comprising at least one polymer selected from the group consisting of an olefin-based polymer, a styrene-based polymer, and a polyester-based polymer, the B layer comprising a vinyl alcohol-based polymer, and the C layer comprising a polymer having a glass transition temperature of −100° C. or more and 5° C. or less.

The structure has few cracks in the layer having heat sealability, and has excellent water vapor barrier properties, heat sealability, and oxygen barrier properties. The reason why the structure has such effects is unclear, but the following reasons are speculated. By using a vinyl alcohol resin with excellent oxygen barrier properties in layer B, the oxygen barrier properties can be improved. However, since vinyl alcohol polymers are resins that undergo relatively large changes in swelling and shrinkage, when layer C is provided on layer B containing a vinyl alcohol polymer, layer C cannot follow the swelling and shrinkage of layer B, and cracks may occur in layer C. Therefore, by using a polymer with a glass transition temperature of -100°C or higher and 5°C or lower inclusive for layer C, i.e., a polymer with a low glass transition temperature, layer C can adequately follow the swelling and shrinkage of layer B. As a result, in the structure, cracks in layer C are suppressed, and water vapor barrier properties can be improved.

As shown in FIG. 1, a structure 10 according to one embodiment of the present invention comprises a paper base material 11, an A layer 12, a B layer 13, and a C layer 14. The structure 10 is a laminate in which the A layer 12, the B layer 13, and the C layer 14 are laminated in this order on one side of the paper base material 11. In the structure 10, the paper base material 11 and the A layer 12, the A layer 12 and the B layer 13, and the B layer 13 and the C layer 14 are directly laminated, respectively. In the structure 10, the C layer 14 is the outermost layer. The structure 10 may be a coated paper.

In an embodiment different from the structure 10 in FIG. 1, layers A, B, and C may be laminated in this order on both sides of the paper substrate. Layers A, B, and C may be laminated in this order on one side of the paper substrate, and one or more of layers A, B, C, or other layers may be laminated on the other side of the paper substrate. Other layers may be present between the paper substrate and layer A, between layers A and B, between layers B and C, and on one or more of the surface of layer C. Each component of the structure will be described in detail below.

(Paper base material)
The paper base material can be a general paper mainly composed of plant-derived pulp. In this specification, the term "main component" refers to the component with the highest content by mass. In addition to pulp, the paper base material may contain sizing agents, fillers, paper strength agents, retention improvers, pH adjusters, drainage improvers, water-resistant agents, softeners, antistatic agents, defoamers, slime control agents, dyes, pigments, etc.

Examples of paper substrates include kraft paper, fine paper, medium-quality paper, alkaline paper, paperboard, glassine paper, semi-glassine paper, parchment paper, etc., with fine paper being preferred.

The basis weight (mass per unit area) of the paper base material is preferably from 20 g/ ^m2 to 500 g/ ^m2 , more preferably from 30 g/ ^m2 to 300 g/ ^m2 , even more preferably from 40 g/ ^m2 to 200 g/ ^m2 , and even more preferably from 50 g/ ^m2 to 100 g/ ^m2 .

The density of the paper base material is preferably from 0.5 g/cm ³ to 1.2 g/cm ³ , and more preferably from 0.6 g/cm ³ to 1.0 g/cm ³ .

The paper base material can be manufactured by a known method. In addition, commercially available paper base materials can be used.

(A layer)
Layer A is a layer that exists between the paper substrate and layer B. Layer A may be laminated directly onto the paper substrate.

(Polymer (a))
The A layer contains at least one selected from the group consisting of an olefin-based polymer, a styrene-based polymer, and a polyester-based polymer (hereinafter also referred to as "polymer (a)"). By containing such a relatively highly hydrophobic polymer (a) in the A layer, the A layer can exhibit good water vapor barrier properties and the like. The polymer (a) is preferably the main component of the A layer. One or more types of polymer (a) can be used.

(Olefin Polymer)
The olefin-based polymer is a polymer containing an olefin as a monomer. The olefin-based polymer may be a polyolefin, which is a polymer of one or more olefins, or a copolymer of one or more olefins and one or more other monomers other than olefins.

Olefins include α-olefins such as ethylene, propylene, n-butene, and isobutylene.

Other monomers than olefins that constitute olefin-based polymers include unsaturated carboxylic acid compounds, diene compounds, vinyl ethers, vinyl halides, vinylidene halides, allyl compounds, etc., with unsaturated carboxylic acid compounds being preferred.

Unsaturated carboxylic acid compounds refer to unsaturated carboxylic acids and compounds in which the hydrogen atom of the carboxy group constituting the unsaturated carboxylic acid has been replaced with another atom or another group. In other words, unsaturated carboxylic acid compounds include unsaturated carboxylic acid, unsaturated carboxylic acid esters, unsaturated carboxylate salts, etc. The unsaturated carboxylic acid compounds are preferably monomers having a carboxy group or salts thereof.

Examples of unsaturated carboxylic acid compounds include unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, itaconic acid monoethyl ester, and fumaric acid monobutyl ester; and unsaturated carboxylates such as sodium (meth)acrylate. Note that "(meth)acrylic acid" means acrylic acid and methacrylic acid.

As the olefin-based polymer, polyolefins and olefin-unsaturated carboxylic acid-based copolymers are preferred, and olefin-unsaturated carboxylic acid-based copolymers are more preferred. An olefin-unsaturated carboxylic acid-based copolymer refers to a copolymer of one or more olefins and one or more unsaturated carboxylic acid-based compounds. Among olefin-unsaturated carboxylic acid-based copolymers, olefin-unsaturated carboxylic acid copolymers, which are copolymers of one or more olefins and one or more unsaturated carboxylic acids, are preferred.

Examples of olefin-unsaturated carboxylic acid copolymers include ethylene-(meth)acrylic acid copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-ethyl (meth)acrylate copolymer, and ethylene-butyl (meth)acrylate copolymer. Among these, ethylene-(meth)acrylic acid copolymer is preferred. Copolymers of ethylene and unsaturated carboxylic acid compounds are also preferred. These copolymers may further be copolymerized with other monomers that are copolymerizable with the olefin and the unsaturated carboxylic acid compound.

(styrene polymer)
A styrene-based polymer is a polymer containing a styrene-based compound as a monomer. The styrene-based compound refers to styrene and a compound in which the hydrogen atoms of styrene are substituted with other atoms or other groups. Examples of the styrene-based compound include styrene, α-methylstyrene, vinyltoluene, and chlorostyrene, with styrene being preferred.

Examples of styrene copolymers include polystyrene, styrene-acrylic copolymers, and styrene-butadiene copolymers.

Styrene-acrylic copolymers are copolymers of the above-mentioned styrene compounds and acrylic compounds. Acrylic compounds refer to (meth)acrylic acid and compounds in which the hydrogen atoms of the carboxy groups constituting (meth)acrylic acid are replaced with other atoms or other groups. Examples of acrylic compounds include (meth)acrylic acid, (meth)acrylic acid esters, and (meth)acrylic acid salts. Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate. Examples of (meth)acrylic acid salts include sodium (meth)acrylate.

Examples of styrene-acrylic copolymers include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid ester copolymers, and styrene-(meth)acrylate copolymers. Other monomers may be further copolymerized in the styrene-acrylic copolymers.

Styrene-butadiene copolymers are copolymers of the above-mentioned styrene compounds and butadiene compounds. Butadiene compounds refer to butadiene and compounds in which the hydrogen atoms of butadiene are replaced with other atoms or groups. Butadiene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, etc., with 1,3-butadiene being preferred.

As the styrene-butadiene copolymer, a styrene-butadiene copolymer is preferable. The styrene-butadiene copolymer may further be copolymerized with other monomers.

As styrene-based polymers, styrene-acrylic copolymers and styrene-butadiene copolymers are preferred.

(Polyester Polymer)
A polyester polymer is a polymer in which one or more types of monomers are polymerized through ester bonds. Examples of the polyester polymer include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyglycolic acid, and aromatic liquid crystal polyester.

Among the polymers (a), from the viewpoint of water vapor barrier properties, etc., olefin-based polymers and styrene-based polymers are preferred, and olefin-based polymers are more preferred.

The lower limit of the content of polymer (a) in layer A is preferably 20% by mass, more preferably 40% by mass, and may be 60%, 70%, 80% or 90% by mass. On the other hand, the upper limit of this content may be 100% by mass, or may be 99%, 90%, 80% or 60% by mass.

(Other components in layer A)
The layer A preferably contains a layered inorganic compound. When the layer A contains a layered inorganic compound, the water vapor barrier properties and the like of the structure can be further improved.

Examples of layered inorganic compounds include micas, talc, montmorillonite, kaolinite, vermiculite, smectite, hectorite, taeniolite, and acid clay. Talc is preferred as the layered inorganic compound used in layer A from the viewpoint of water vapor barrier properties, etc. One or more types of layered inorganic compounds can be used.

When layer A contains a layered inorganic compound such as talc, the lower limit of the content of the layered inorganic compound in layer A is preferably 1 mass%, more preferably 5 mass%, and even more preferably 10 mass%, 20 mass%, or 30 mass%. On the other hand, the upper limit of this content is preferably 80 mass%, more preferably 70 mass%, and even more preferably 60 mass%, 50 mass%, or 40 mass%. By setting the content of the layered inorganic compound in layer A within the above range, the water vapor barrier properties, etc. can be further improved.

The A layer may further contain other components in addition to the polymer (a) and the layered inorganic compound. Examples of other components include resins other than the polymer (a), dispersants, surfactants, defoamers, dyes, thickeners, etc. However, the total content of the polymer (a) and any layered inorganic compound in the A layer is preferably 90% by mass or more, more preferably 95% by mass or more or 99% by mass or more. In addition, in the A layer, the content of the cationic resin may be preferably 10% by mass or less, and may be more preferably 5% by mass or less, 1% by mass or less, or 0.5% by mass or less.

The mass per unit area of one A layer is preferably 1 g/m ² or more and 100 g/m ² or less, more preferably 3 g/m ² or more and 50 g/m ² or less, even more preferably 5 g/m ² or more and 30 g/m ² or less, even more preferably 7 g/m ² or more and 20 g/m ² or less, and particularly preferably 9 g/m ² or more and 15 g/m ² or less. When the mass per unit area of one A layer is equal to or more than the lower limit, the water vapor barrier property and the like can be further improved. On the other hand, when the mass per unit area of one A layer is equal to or less than the upper limit, the structure can be made thinner.

(B layer)
The layer B is a layer that is present between the layer A and the layer C. The layer B may be a layer that is directly laminated onto the layer A.

(Polymer (b))
The B layer contains a vinyl alcohol polymer (hereinafter also referred to as "polymer (b)"). When the structure has a B layer containing polymer (b), it can exhibit excellent oxygen barrier properties. The polymer (b) is preferably the main component of the B layer. The polymer (b) is a polymer having a vinyl alcohol unit (-CH ₂ -CHOH-). The polymer (b) is usually obtained by saponification of a vinyl ester polymer. One or more types of polymer (b) can be used.

The lower limit of the saponification degree of polymer (b) is preferably 80 mol%, more preferably 90 mol%, and in some cases 95 mol%, 97 mol%, 98 mol% or 99 mol% are even more preferable. By having a saponification degree equal to or higher than the above lower limit, the oxygen barrier properties and the like can be further improved. On the other hand, the upper limit of the saponification degree may be 100 mol% or 99.9 mol%. The saponification degree of polymer (b) is measured in accordance with JIS K 6726:1994.

The viscosity average degree of polymerization of polymer (b) is preferably 200 or more and 3,000 or less. The lower limit of the viscosity average degree of polymerization may be 300, 500, or 800. On the other hand, the upper limit of the viscosity average degree of polymerization may be 2,500, 2,000, 1,200, or 800. By having the viscosity average degree of polymerization of polymer (b) within the above range, the oxygen barrier properties and the like can be further improved, and the coatability when layer B is provided by coating, the strength of layer B, and the like are also optimized.

The viscosity average degree of polymerization of the polymer (b) is measured in accordance with JIS K 6726:1994. Specifically, the intrinsic viscosity [η] (liters/g) of the polymer (b) is measured in water at 30° C., and the viscosity average degree of polymerization P is calculated by the following formula using the intrinsic viscosity [η] value. When the degree of saponification of the polymer (b) is less than 99.5 mol%, the polymer is saponified to a degree of saponification of 99.5 mol% or more, and then the intrinsic viscosity [η] is measured.
P = ([η] × 10 ⁴ / 8.29) ^(1/0.62)

Polymer (b) may have monomer units derived from other monomers than vinyl alcohol units and vinyl ester units. Examples of other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; (meth)acrylic acid and its salts; (meth)acrylic acid esters; (meth)acrylamide; (meth)acrylamide derivatives such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidopropanesulfonic acid and its salts, (meth)acrylamidopropyldimethylamine and its salts or its quaternary salts, and N-methylol(meth)acrylamide and its derivatives; methyl vinyl ether, ethyl vinyl ether, Examples include vinyl ethers such as n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids and their salts or esters such as maleic acid, itaconic acid, and fumaric acid; vinyl silyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

As the other monomer, an α-olefin is preferable, and ethylene is more preferable. That is, polymer (b) is preferably an α-olefin modified vinyl alcohol polymer, and more preferably an ethylene modified vinyl alcohol polymer. By using such a modified vinyl alcohol polymer, the oxygen barrier properties, etc. can be further improved.

The lower limit of the content of α-olefin units relative to all monomer units in the α-olefin modified vinyl alcohol polymer is preferably 0.1 mol%, more preferably 1 mol%, and may be 2 mol%, 5 mol%, or 7 mol%. On the other hand, the upper limit of this content may be 30 mol%, or may be 20 mol%, 15 mol%, or 12 mol%. The content of α-olefin units relative to all monomer units is also referred to as the α-olefin modification amount. For example, the content of ethylene units relative to all monomer units is also referred to as the ethylene modification amount.

The total content of vinyl alcohol units, vinyl ester units, and any α-olefin units relative to the total monomer units of polymer (b) is preferably 95 mol% or more, more preferably 99 mol% or more, and may be 100 mol%.

Polymer (b) may be used in a mixture of two or more kinds. For example, polymer (b) may be made of two or more kinds of vinyl alcohol-based polymers with different degrees of polymerization. A vinyl alcohol-based polymer with a low degree of polymerization has low viscosity and is excellent in coatability. On the other hand, a vinyl alcohol-based polymer with a high degree of polymerization has excellent strength, etc. Therefore, by mixing two or more kinds of vinyl alcohol-based polymers with different degrees of polymerization, it is possible to achieve a balance between these properties. Note that a vinyl alcohol-based polymer made of two or more kinds with different degrees of polymerization may have two or more peaks in a molecular weight distribution curve obtained by GPC (gel permeation chromatography) analysis.

The lower limit of the content of polymer (b) in layer B is preferably 70% by mass, more preferably 80% by mass, and even more preferably 90% by mass. By making the content of polymer (b) in layer B equal to or greater than the above lower limit, the oxygen barrier properties and the like can be further improved. On the other hand, the upper limit of this content may be 100% by mass, 99% by mass, or 97% by mass.

(Other components in layer B)
Layer B preferably contains a layered inorganic compound. When layer B contains a layered inorganic compound, the oxygen barrier properties and the like of the structure can be further improved.

The layered inorganic compound may be the same as those exemplified in the description of the A layer. As the layered inorganic compound used in the B layer, mica is preferred from the viewpoint of oxygen barrier properties, etc. One or more types of layered inorganic compounds may be used.

When layer B contains a layered inorganic compound such as mica, the lower limit of the amount of the layered inorganic compound in layer B is preferably 1 mass%, and more preferably 3 mass%. On the other hand, the upper limit of this amount is preferably 30 mass%, more preferably 20 mass%, and even more preferably 10 mass%. By setting the amount of the layered inorganic compound in layer B within the above range, the oxygen barrier properties, etc. can be further improved.

Layer B may further contain other components in addition to the polymer (b) and the layered inorganic compound. Examples of other components include resins other than the polymer (b), dispersants, surfactants, defoamers, dyes, thickeners, etc. However, the total content of the polymer (b) and any layered inorganic compound in layer B is preferably 90% by mass or more, more preferably 95% by mass or more or 99% by mass or more.

The mass per unit area of one B layer is preferably 0.3 g/m ² or more and 20 g/m ² or less, more preferably 0.5 g/m ² or more and 10 g/m ² or less, even more preferably 1 g/m ² or more and 7 g/m ² or less, and even more preferably 2 g/m ² or more and 5 g/m ² or less. When the mass per unit area of one B layer is equal to or more than the above lower limit, the oxygen barrier property can be further improved. On the other hand, when the mass per unit area of one B layer is equal to or less than the above upper limit, the structure can be made thinner.

(C layer)
The layer C is a layer present on the opposite side of the layer B from the layer A. The layer C may be a layer directly laminated on the layer B. The layer C may also be the outermost layer.

(Polymer (c))
The C layer contains a polymer having a glass transition temperature of −100° C. or more and 5° C. or less (hereinafter, also referred to as “polymer (c)”). The polymer (c) is preferably the main component of the C layer. The polymer (c) can be used alone or in combination of two or more kinds.

The upper limit of the glass transition temperature of polymer (c) is 5°C, preferably 3°C, more preferably 2°C, and even more preferably 1°C, 0°C, -1°C, -3°C, -5°C or -10°C. By having the glass transition temperature of polymer (c) equal to or lower than the above upper limit, cracking of layer C is suppressed and the water vapor barrier properties can be improved. On the other hand, the lower limit of this glass transition temperature is -100°C, and may be -80°C, -60°C, -50°C or -40°C.

The upper limit of the melting point of polymer (c) may be 120°C, but is preferably 100°C, more preferably 85°C, even more preferably 80°C, and even more preferably 75°C, 70°C or 65°C. By having the melting point of polymer (c) below the above upper limit, the heat sealability can be improved. The melting point of polymer (c) may be less than 80°C. On the other hand, the lower limit of this melting point is preferably 30°C, more preferably 40°C, and even more preferably 50°C.

The glass transition temperature and melting point of polymer (c) are measured by differential scanning calorimetry (DSC). Specifically, they can be measured by the method described in the Examples.

The polymer (c) is not particularly limited as long as it is a polymer having a glass transition temperature of -100°C or more and 5°C or less. For example, the polymer (c) may be any of the olefin-based polymers, styrene-based polymers, and polyester-based polymers described as polymer (a) that have a glass transition temperature of -100°C or more and 5°C or less.

As the polymer (c), olefin-based polymers and styrene-based polymers are preferred, styrene-based polymers are more preferred, styrene-acrylic copolymers and styrene-butadiene copolymers are even more preferred, styrene-acrylic copolymers are even more preferred, and styrene-(meth)acrylic acid ester copolymers are particularly preferred. Among the olefin-based polymers, olefin-unsaturated carboxylic acid copolymers are preferred, olefin-unsaturated carboxylic acid copolymers are more preferred, and ethylene-(meth)acrylic acid copolymers are even more preferred. As the polymer (c), a copolymer of a hydrocarbon-based monomer and an acrylic compound is also preferred. Examples of the hydrocarbon-based monomer include the above-mentioned olefins and styrene-based compounds. By using such a polymer as the polymer (c), the water vapor barrier properties, heat sealability, and the like can be further improved. The specific forms of the olefin-based polymers and styrene-based polymers as the polymer (c) are the same as those described above for the olefin-based polymers and styrene-based polymers in the polymer (a).

In one embodiment of the present invention, polymer (a) and polymer (c) may be the same type of polymer or different types of polymer. For example, in order to optimize the functions of layers A and C, different types of polymers may be used for polymer (a) and polymer (c).

The lower limit of the content of polymer (c) in layer C is preferably 50% by mass, more preferably 60% by mass, even more preferably 70% by mass, and even more preferably 80% by mass, 85% by mass, or 90% by mass. On the other hand, the upper limit of this content is preferably 100% by mass, more preferably 99% by mass, and even more preferably 95% by mass.

(Other components in layer C)
The layer C preferably contains a wax. When the layer C contains a wax, the water vapor barrier property can be further improved, etc. Also, when the layer C contains a wax, the oil resistance, etc. tends to be improved.

The wax preferably contains paraffin wax. For example, paraffin wax containing normal paraffin as the main component, which has a carbon number of 20 to 40 and a molecular weight of 300 to 500, can be used. Commercially available paraffin wax can be used.

When the C layer contains wax, the lower limit of the wax content in the C layer may be, for example, 0.1% by mass, but is preferably 1% by mass, more preferably 3% by mass, and even more preferably 5% by mass. On the other hand, the upper limit of this content may be, for example, 30% by mass, but is preferably 20% by mass, more preferably 15% by mass, and even more preferably 12% by mass. By setting the wax content in the C layer within the above range, the water vapor barrier property and the like can be further improved. Furthermore, when the C layer contains paraffin wax, the lower limit of the paraffin wax content in the C layer may be, for example, 0.1% by mass, but is preferably 1% by mass, more preferably 3% by mass, and even more preferably 5% by mass. On the other hand, the upper limit of this content may be, for example, 30% by mass, but is preferably 20% by mass, more preferably 15% by mass, and even more preferably 12% by mass. By setting the paraffin wax content in the C layer within the above range, the water vapor barrier property and the like can be further improved.

The C layer may further contain other components in addition to the polymer (c) and the wax. Examples of other components include resins other than the polymer (c), dispersants, surfactants, defoamers, dyes, thickeners, etc. The C layer may contain two or more polymers. The two or more polymers that may be contained in the C layer may be a combination of the polymer (c) and another polymer, or may be two or more polymers (c). However, the total content of the polymer (c) and any wax in the C layer is preferably 90% by mass or more, more preferably 95% by mass or more or 99% by mass or more.

In particular, it is preferable that the C layer does not substantially contain a vinyl alcohol-based polymer. The content of the vinyl alcohol-based polymer in the C layer is preferably 10 mass % or less, more preferably 3 mass % or less, even more preferably 1 mass % or less, and even more preferably 0.1 mass % or less. By reducing the content of the vinyl alcohol-based polymer in the C layer in this way, it is possible to suppress an increase in the viscosity of the coating liquid for forming the C layer when the C layer is provided by coating, and it is possible to form the C layer efficiently.

The C layer preferably has a melting point of 120°C or less. The upper limit of the melting point of the C layer is preferably 100°C, more preferably 85°C, even more preferably 80°C, and even more preferably 75°C, 70°C, or 65°C. By having the melting point of the C layer be equal to or less than the above upper limit, the heat sealability can be improved. The C layer may have a melting point less than 80°C. On the other hand, the lower limit of the melting point is preferably 30°C, more preferably 40°C, and even more preferably 50°C. The melting point of the C layer is measured by differential scanning calorimetry (DSC). Note that, when one of the components (polymer (c) and other optional components) contained in the C layer has a specified melting point T, the C layer usually also has the same specified melting point T.

The mass per unit area of one C layer is preferably 1 g/m ² or more and 100 g/m ² or less, more preferably 3 g/m ² or more and 50 g/m ² or less, even more preferably 5 g/m ² or more and 30 g/m ² or less, even more preferably 7 g/m ² or more and 20 g/m ² or less, and particularly preferably 9 g/m ² or more and 15 g/m ² or less. When the mass per unit area of one C layer is equal to or more than the lower limit, the water vapor barrier property can be further improved. On the other hand, when the mass per unit area of one C layer is equal to or less than the upper limit, the structure can be made thinner.

The structure can be suitably used as grease-resistant paper, gas barrier paper, flavor barrier paper, packaging material, etc. The structure can also be used in a state where it is formed into a predetermined shape (e.g., a bag shape) by heat sealing the C layers together. There are no particular limitations on the heat sealing method, and any known method can be used, for example, heat sealing can be performed using a hot plate heat sealer, impulse sealer, ultrasonic sealer, frictional heat sealer, dielectric heating sealer, etc.

<Method of Manufacturing Structure>
The method for producing the structure according to one embodiment of the present invention is not particularly limited, but typically, the structure can be produced by providing an A layer, a B layer, and a C layer in this order on a paper substrate by coating. Specifically, for example, an A layer forming coating liquid is applied to the surface of the paper substrate and dried to provide an A layer. Next, a B layer forming coating liquid is applied to the surface of the A layer and dried to provide a B layer. Next, a C layer forming coating liquid is applied to the surface of the B layer and dried to provide a C layer, thereby obtaining a structure. Drying is not required after each coating of the coating liquid, and a simultaneous multi-layer coating method may be adopted.

Each coating liquid can be applied by a conventional method. For example, coating can be performed using a blade coater, bar coater, air knife coater, slit die coater, gravure coater, microgravure coater, gate roll coater, curtain coater, etc. Among these, it is preferable to use a curtain coater.

In other words, the method for manufacturing a structure according to one embodiment of the present invention includes a step of forming at least one of the layers A, B, and C using a curtain coater. In this manufacturing method, it is preferable to form all of the layers A, B, and C using a curtain coater.

The method for drying the applied coating liquid is not particularly limited, and can be done using, for example, a hot air dryer, an infrared dryer, a gas burner, a hot plate, etc.

The solvent or dispersion medium for the coating liquid used to form each layer is not particularly limited, and water or an organic solvent (ethanol, isopropyl alcohol, methyl ethyl ketone, toluene, etc.) can be used, with water being preferred.

The solid content (solid content concentration) of the coating liquid for forming each layer is not particularly limited, but can be, for example, 3% by mass or more and 70% by mass or less, 5% by mass or more and 60% by mass or less, or 10% by mass or more and 50% by mass or less.

<Oil-resistant paper>
The grease-resistant paper according to one embodiment of the present invention includes the structure according to one embodiment of the present invention. The grease-resistant paper according to one embodiment of the present invention may be made of the structure according to one embodiment of the present invention.

This grease-resistant paper has excellent water vapor barrier properties and oxygen barrier properties, and when there are heat-sealed parts, the adhesion is also good. This grease-resistant paper is ideally used as a packaging material for serving oily foods such as French fries and fried chicken, a packaging material for wrapping butter, and cooking paper for baking bread, cakes, etc.

The oil resistance (KIT value) of the oil-resistant paper is preferably grade 5 or higher, and more preferably grade 6 or 7 or higher. This oil resistance is the value measured on the surface of layer C using the TAPPI UM-557 method (KIT method).

<Gas barrier paper>
The gas barrier paper according to one embodiment of the present invention includes the structure according to one embodiment of the present invention. The gas barrier paper according to one embodiment of the present invention may be made of the structure according to one embodiment of the present invention.

This gas barrier paper has excellent oxygen and water vapor barrier properties, and when there are heat-sealed parts, the adhesion is also good. This gas barrier paper is suitable for use as a packaging material for food, pesticides, medicines, cosmetics, medical products, electronic parts, clothing, etc.

The oxygen permeability of the gas barrier paper is preferably 10 cc/ ^m2 ·24h or less, more preferably 5 cc/ ^m2 ·24h or less, and even more preferably 3 cc/ ^m2 ·24h or less. The oxygen permeability is a value measured under conditions of 23°C and 65% RH.

<Flavor barrier paper>
The flavour barrier paper according to an embodiment of the present invention comprises a structure according to an embodiment of the present invention. The flavour barrier paper according to an embodiment of the present invention may consist of a structure according to an embodiment of the present invention.

This flavor barrier paper has excellent oxygen and water vapor barrier properties, and when there are heat-sealed sections, the adhesion is also good. This flavor barrier paper is suitable for use as a packaging material for items that have a scent, such as confectionery, tea leaves, coffee, spices, tobacco, cosmetics, fragrances, etc. This flavor barrier paper is also useful as a packaging material for other foods, pesticides, medicines, clothing, etc.

Generally, when the oxygen permeability is low, the property of blocking aromas also tends to be high. The oxygen permeability of the flavor barrier paper is preferably 10 cc/ ^m2 ·24 h or less, more preferably 5 cc/ ^m2 ·24 h or less, and even more preferably 3 cc/ ^m2 ·24 h or less.

<Packaging materials>
The packaging material according to one embodiment of the present invention includes at least one selected from the group consisting of the greaseproof paper according to one embodiment of the present invention, the gas barrier paper according to one embodiment of the present invention, and the flavor barrier paper according to one embodiment of the present invention. The packaging material according to one embodiment of the present invention may include the structure according to one embodiment of the present invention.

The packaging material has excellent water vapor barrier properties and oxygen barrier properties, and when there are heat-sealed parts, the adhesion is also good. The packaging material is suitable for use as packaging for, for example, food, pesticides, medicines, cosmetics, medical products, electronic parts, clothing, etc.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

[Production Example 1] Production of PVA-1 1,050g of vinyl acetate and 1,950g of methanol were charged into a reaction vessel equipped with a stirrer, a nitrogen inlet and an initiator addition port, and the temperature was raised to 60°C, after which the system was replaced with nitrogen by nitrogen bubbling for 30 minutes. After adjusting the temperature inside the reaction vessel to 60°C, 1.6g of azobisisobutyronitrile (AIBN) was added as a polymerization initiator to start polymerization. After 3 hours, when the polymerization rate reached 50%, the polymerization was stopped by cooling. Unreacted vinyl acetate monomer was removed, and methanol was added to obtain a methanol solution of polyvinyl acetate (PVAc) (concentration 30% by mass). 55.8g of a 10% methanol solution of NaOH (molar ratio [MR] of the amount of NaOH to the vinyl acetate unit in PVAc: 0.10) was added to 400g of the methanol solution of PVAc (120g of PVAc in the solution), and saponification was carried out at 40°C. After the addition of the NaOH methanol solution, the gel was pulverized in a pulverizer and subjected to a saponification reaction for a total of 1 hour. Then, 1,000 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, 1,000 g of methanol was added to the white solid obtained by filtration and left to stand at room temperature for 3 hours for washing. After repeating the above washing operation three times, the solid obtained by centrifugal deliquor was left to stand in a dryer at 70°C for 2 days to dry, thereby obtaining a vinyl alcohol polymer (PVA-1).

[Production Example 2] Production of PVA-2 1,440 g of vinyl acetate and 1,560 g of methanol were charged into a 5 L pressurized reaction vessel equipped with a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition port, and the temperature was raised to 60 ° C., and the system was replaced with nitrogen by nitrogen bubbling for 30 minutes. Then, ethylene was introduced so that the reaction vessel pressure was 7.8 kg / cm ^2. After adjusting the temperature inside the reaction vessel to 60 ° C., 2.0 g of AIBN was added as a polymerization initiator to start polymerization. During polymerization, ethylene was introduced to maintain the reaction vessel pressure at 7.8 kg / cm ² and the polymerization temperature at 60 ° C. After 3 hours, when the polymerization rate reached 50%, the polymerization was stopped by cooling. After opening the reaction vessel and removing ethylene, nitrogen gas was further bubbled. Next, unreacted vinyl acetate monomer was removed under reduced pressure, and methanol was added to obtain a methanol solution of ethylene-vinyl acetate copolymer (concentration 30 mass %). To 400 g of the methanol solution of the ethylene-vinyl acetate copolymer (120 g of the ethylene-vinyl acetate copolymer in the solution), 55.8 g of a 10% methanol solution of NaOH (molar ratio [MR] of the amount of NaOH to the vinyl acetate unit in the ethylene-vinyl acetate copolymer: 0.10) was added, and saponification was carried out at 40° C. After the addition of the NaOH methanol solution, the gel was pulverized in a grinder, and a saponification reaction was carried out for a total of 1 hour. Thereafter, 1,000 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, 1,000 g of methanol was added to the white solid obtained by filtration, and the solid was left to stand at room temperature for 3 hours for washing. The above washing operation was repeated three times, and the solid obtained by centrifugal deliquation was left to stand in a dryer at 70° C. for 2 days to obtain an ethylene-modified vinyl alcohol polymer (PVA-2).

Production Example 3-5: Production of PVA-3 to PVA-5 Each ethylene-modified vinyl alcohol polymer (PVA-3 to PVA-5) was produced in the same manner as in Production Example 2, except that the polymerization conditions and saponification conditions shown in Table 1 were changed to those shown in Table 1.

The viscosity average degree of polymerization, degree of saponification, and amount of ethylene modification (ethylene unit content) of the obtained PVA-1 to PVA-5 were measured. The results of these measurements are shown in Table 1.

The polymers other than PVA-1 to PVA-5 used in the examples and comparative examples are shown below.
(Polymer (a))
Polymer a1: "MFP1883" (manufactured by Michelman, Inc.), olefin-acrylic acid copolymer emulsion, solid content 27% by mass
Polymer a2: "OP-671" (manufactured by Lion Corporation), styrene-acrylic acid ester copolymer emulsion, solid content 48% by mass
Polymer a3: "Chemipearl S-100" (manufactured by Mitsui Chemicals, Inc.), ethylene-methacrylic acid copolymer emulsion, solid content 27% by mass
Polymer a4: "Tykote 1004" (Mallard Creek Polymers, Inc.) Styrene-butadiene copolymer emulsion

(Polymer (b))
PU-1: "Takelac WPB-341" (manufactured by Mitsui Chemicals, Inc.), polyurethane emulsion, solid content 30% by mass

(Polymer (c))
Polymer c1: "VAPCT2200" (manufactured by Michelman, Inc.), styrene-acrylic acid ester copolymer emulsion, solid content 48% by mass, glass transition temperature -32.3°C, melting point 60.4°C
Polymer c2: "498340R" (manufactured by Michelman, Inc.), ethylene-acrylic acid copolymer emulsion, solid content 40% by mass, glass transition temperature -0.5°C, melting point 78.7°C
Polymer c3: "OP-671" (manufactured by Lion Corporation), styrene-butadiene copolymer emulsion, solid content 48% by mass, glass transition temperature 2.8°C, melting point 47.0°C
Polymer c4: "Chemipearl S-100" (manufactured by Mitsui Chemicals, Inc.), ethylene-methacrylic acid copolymer emulsion, solid content 27% by mass, glass transition temperature 23.9°C, melting point 86.9°C

(Method of measuring glass transition temperature and melting point)
The glass transition temperature and melting point of the polymer (C) were measured by the following method.
Approximately 3 mg of the measurement sample was filled into a sample pan, and the glass transition point and melting point were measured using a DSC Q2000 (manufactured by TA Instruments, Inc.). The sample was heated from 30° C. to 200° C., then cooled to −90° C., held at that temperature for 5 minutes, and then heated to 200° C. The temperature was increased and decreased at a rate of 10° C./min.

[Example 1] Preparation of structure A fine paper with a basis weight of 70.5 g/m ² was prepared as a paper substrate. On one side of this paper substrate, "MFP1883", an emulsion of polymer a1, was applied as a coating liquid for forming an A layer in a coating amount of 10.0 g/m ² in dry mass, and dried to provide an A layer. Next, on the surface of the A layer, an aqueous solution of PVA-1 (solid content 10% by mass) was applied as a coating liquid for forming a B layer in a coating amount of 3.0 g/m ² in dry mass, and dried to provide a B layer. Next, on the surface of the B layer, "VAPCT2200", an emulsion of polymer c1, was applied as a coating liquid for forming a C layer in a coating amount of 10.0 g/m ² in dry mass, and dried to provide a C layer. Thus, the structure of Example 1 was obtained. Coating of the A layer, B layer, and C layer was all performed using a wire bar. The obtained structure and the coating solution for forming the C layer used were subjected to the following evaluations. The evaluation results are shown in Table 3.

[evaluation]
(1) Viscosity of Coating Liquid for Forming C Layer After adjusting the temperature of the coating liquid for forming C layer in a room of 20° C., the viscosity of the coating liquid for forming C layer was measured at 60 rpm using a Brookfield viscometer.

(2) Viscosity Stability of Coating Liquid for Forming C Layer The coating liquid for forming C layer was adjusted to a solid content of 22% by mass, and the fluidity of this coating liquid when stirred was evaluated according to the following criteria.
A: Flows without thickening.
B: The mixture thickens but remains fluid.
C: Fluidity is impaired (becomes creamy).

(3) Oxygen permeability (gas barrier properties)
The oxygen permeability of the structure was measured under conditions of 23° C. and 65% RH using “OX-TRAN2/21” manufactured by MOCON Corporation.

(4) Water vapor permeability (water vapor barrier property)
The water vapor permeability of the structure was measured by the cup method based on JIS Z 2080 under conditions of a temperature of 40±0.5° C. and a relative humidity difference of 90±2%.

(5) Cracking in Layer C The presence or absence and the degree of cracking in Layer C of the structure was visually evaluated according to the following criteria.
A ⁺ : No cracks observed.
A: Partial cracks are observed.
B: Partial continuous cracks are observed.
C: Continuous cracks are observed throughout the entire surface.

(6) Heat sealability The C layers of the structures were overlapped and heat sealed using a thermal gradient tester under conditions of 160°C, 0.3 MPa, and 1 second. Then, a 180° peel test was performed using an autograph, and the breakage point was evaluated according to the following criteria.
A: Damage to the paper base material (strength between layers C is greater than or equal to the paper base material and is sufficiently strong)
B: Interlayer delamination (sealed, but weaker than the strength of the paper base material)
C: Natural peeling (unsealed state)

[Example 2]
The structure of Example 2 was obtained in the same manner as in Example 1, except that PVA-2 was used instead of PVA-1 in the coating liquid for forming the B layer, and "498340R", an emulsion of polymer c2, was used as the coating liquid for forming the C layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 3]
The structure of Example 3 was obtained in the same manner as in Example 2, except that "OP-671", an emulsion of polymer c3, was used as the coating liquid for forming the C layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 4]
A paraffin wax emulsion "Haricoat RT" (manufactured by Harima Chemical Group Co., Ltd.) was added to an emulsion of polymer c1 "VAPACT 2200" to prepare a mixed solution in which the solid content of "Haricoat RT" per polymer c1 (100 parts by mass) was 0.5 parts by mass. The same operation as in Example 2 was carried out except that this mixed solution was used as the coating liquid for forming the C layer, to obtain the structure of Example 4. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 5]
The same operation as in Example 4 was performed except that the content of "Haricoat RT" in terms of solid content relative to the polymer c1 (100 parts by mass) in the coating liquid for forming the C layer was 10 parts by mass, to obtain a structure of Example 5. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 6]
The same operation as in Example 4 was performed except that the content of "Haricoat RT" in terms of solid content relative to the polymer c1 (100 parts by mass) in the coating liquid for forming the C layer was 22 parts by mass, to obtain a structure of Example 6. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 7]
The structure of Example 7 was obtained in the same manner as in Example 5, except that "OP-671", an emulsion of polymer a2, was used as the coating liquid for forming layer A. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 8]
The structure of Example 8 was obtained in the same manner as in Example 5, except that "Chemipearl S-100", an emulsion of polymer a3, was used as the coating liquid for forming layer A. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 9]
The structure of Example 9 was obtained in the same manner as in Example 5, except that "Tykote 1004", an emulsion of polymer a4, was used as the coating liquid for forming the A layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 10]
A talc dispersion "Finntalc C10B" (manufactured by Elementis) was added to an emulsion of polymer a1, "MFP1883," to prepare a mixed solution in which the talc content was 50 parts by mass relative to polymer a1 (100 parts by mass). The same operation as in Example 5 was carried out except that this mixed solution was used as the coating solution for forming layer A, to obtain a structure of Example 10. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 11]
A mica dispersion "ME-100" (manufactured by Katakura Co-op Agri Co., Ltd.) was added to an aqueous solution of PVA-2 (solid content 10% by mass) to prepare a mixed solution in which the mica content was 5 parts by mass relative to PVA-2 (100 parts by mass). The same operation as in Example 5 was carried out except that this mixed solution was used as the coating solution for forming B layer, to obtain a structure of Example 11. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 12]
The same procedure as in Example 5 was carried out except that PVA-3 was used instead of PVA-2 in the coating liquid for forming the B layer, to obtain a structure of Example 12. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 13]
The same procedure as in Example 5 was carried out except that PVA-4 was used instead of PVA-2 in the coating liquid for forming the B layer, to obtain a structure of Example 13. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Example 14]
A mica dispersion "ME-100" (manufactured by Katakura Co-op Agri Co., Ltd.) was added to an aqueous solution of PVA-2 (solid content 10% by mass) to prepare a mixed solution in which the mica content was 5 parts by mass relative to PVA-2 (100 parts by mass). The same operation as in Example 10 was carried out except that this mixed solution was used as the coating solution for forming B layer, to obtain the structure of Example 14. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Comparative Example 1]
A structure of Comparative Example 1 was obtained in the same manner as in Example 5, except that "Chemipearl S-100", an emulsion of polymer c4, was used as the coating liquid for forming the C layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Comparative Example 2]
A structure of Comparative Example 2 was obtained in the same manner as in Example 2, except that "Chemipearl S-100", an emulsion of polymer c4, was used as the coating liquid for forming the C layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Comparative Example 3]
PVA-5 was added to "Chemipearl S-100", an emulsion of polymer c4, to prepare a mixed solution in which the content of PVA-5 was 5 parts by mass relative to polymer c4 (100 parts by mass). The same operation as in Comparative Example 2 was carried out except that this mixed solution was used as the coating solution for forming C layer, to obtain a structure of Comparative Example 3. Evaluation was carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

[Comparative Example 4]
A structure of Comparative Example 4 was obtained in the same manner as in Comparative Example 2, except that "Takelac WPB-341", an emulsion of PU-1, was used as the coating liquid for forming the B layer. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

The structures of Examples 1 to 14, in which Layer B contains vinyl alcohol polymers (PVA-1 to PVA-4) and Layer C contains polymers (Polymers c1 to c3) with glass transition temperatures of -100°C or higher and 5°C or lower, showed little cracking in Layer C and excellent water vapor barrier properties, heat sealability, and oxygen barrier properties. In particular, by comparing Examples 2 and 3 with Comparative Example 2, which differ only in the type of polymer (c), it can be confirmed that the glass transition temperature of the polymer (c) that constitutes Layer C has a significant effect on the occurrence of cracking and water vapor barrier properties of Layer C.

When layer B does not contain a vinyl alcohol-based polymer, as in Comparative Example 4, the oxygen barrier property is low, but cracks in layer C are unlikely to occur even if the glass transition temperature of the polymer contained in layer C is high. In contrast, when layer B contains a vinyl alcohol-based polymer, as in Comparative Examples 1 and 2, cracks occur in layer C depending on the glass transition temperature of the polymer contained in layer C, and the water vapor barrier property is low. In this way, it can be confirmed that cracks in layer C are a phenomenon that occurs significantly when layer B contains a vinyl alcohol-based polymer. In other words, in the structures of Examples 1 to 14, a vinyl alcohol-based polymer with particularly high oxygen barrier property is used in layer B, and a polymer that is unlikely to crack is used in layer C, making it possible to achieve both excellent oxygen barrier property and water vapor barrier property.

Furthermore, when the coating liquid for forming the C layer contains a vinyl alcohol polymer, as in Comparative Example 3, the viscosity becomes high and the viscosity stability becomes low, resulting in poor coatability.

The structure of the present invention can be suitably used as packaging materials such as grease-resistant paper, gas barrier paper, and flavor barrier paper.

10 Structure 11 Paper base material 12 A layer 13 B layer 14 C layer

Claims

A structure in which an A layer, a B layer, and a C layer are laminated in this order on at least one surface of a paper substrate,
The layer A contains at least one selected from the group consisting of an olefin-based polymer, a styrene-based polymer, and a polyester-based polymer,
The layer B contains a vinyl alcohol polymer,
The structure, wherein the layer C contains a polymer having a glass transition temperature of -100°C or higher and 5°C or lower.
The structure described in claim 1, wherein the C layer has a melting point of 120°C or less.
The layer A contains the olefin polymer,
3. The structure according to claim 1, wherein the olefin polymer comprises an olefin-unsaturated carboxylic acid copolymer.
The structure according to claim 1, claim 2 or claim 3, wherein the A layer further contains talc.
The structure according to claim 4, wherein the talc content in layer A is 1% by mass or more and 80% by mass or less.
The structure according to any one of claims 1 to 5, wherein the vinyl alcohol polymer is an ethylene-modified vinyl alcohol polymer.
The structure according to any one of claims 1 to 6, wherein the polymer having a glass transition temperature of -100°C or more and 5°C or less is a styrene-acrylic copolymer.
The structure according to any one of claims 1 to 7, wherein the C layer further contains wax.
The structure according to claim 8, wherein the wax content in the C layer is 0.1% by mass or more and 30% by mass or less.
The structure according to claim 8 or claim 9, wherein the wax comprises paraffin wax.
The structure according to claim 10, wherein the content of the paraffin wax in the C layer is 1% by mass or more and 30% by mass or less.
The structure according to any one of claims 1 to 11, wherein the vinyl alcohol polymer is made of two or more types of vinyl alcohol polymers having different degrees of polymerization.
The structure according to any one of claims 1 to 12, wherein the A layer contains at least two types selected from the group consisting of the olefin-based polymer, the styrene-based polymer, and the polyester-based polymer.
The structure according to any one of claims 1 to 13, wherein the C layer contains two or more types of polymers.
A method for producing the structure according to any one of claims 1 to 14,
A method for manufacturing a structure, comprising a step of providing at least one of the A layer, B layer, and C layer using a curtain coater.
　Grease-resistant paper comprising the structure described in any one of claims 1 to 14.
Gas barrier paper comprising the structure described in any one of claims 1 to 14.
Flavor barrier paper comprising the structure described in any one of claims 1 to 14.
A packaging material comprising at least one selected from the group consisting of the grease-resistant paper according to claim 16, the gas barrier paper according to claim 17, and the flavor barrier paper according to claim 18.